1. Field of the Invention
The present invention relates to a solid state electrolytic capacitor and a method of forming the same, and more particularly to a solid state electrolytic capacitor with an improved anode lead terminal and a method of forming the same.
2. Description of the Related Art
A chip type solid state electrolytic capacitor has been known as one of the solid state electrolytic capacitors. FIG. 1 is a schematic perspective view of a partial internal structure of a conventional chip type solid state electrolytic capacitor. FIG. 2 is a cross sectional elevation view of the conventional chip type solid state electrolytic capacitor of FIG. 1. The internal structure of the conventional chip type solid state electrolytic capacitor will hereinafter be described with reference to FIGS. 1 and 2.
The chip type solid state electrolytic capacitor 7 has a cathode lead terminal 1, a device pellet 3, and an anode lead terminal 6. The device pellet 3 has a cathode layer. The cathode lead terminal 1 is adhered via an electrically conductive adhesive agent 8 to the cathode layer of the device pellet 3. The device pellet 3 also has an pellet lead wire 4 which is welded through a weld-bonding portion 5 to the anode lead terminal 6. The capacitor 7 is encapsulated with an encapsulating resin 2, wherein respective parts of the cathode lead terminal 1 and the anode lead terminal 6 are exposed from the encapsulating resin 2. The exposed parts of the cathode lead terminal 1 and the anode lead terminal 6 extend along opposite side walls of the encapsulating resin 2 and along bottom recesses of the encapsulating resin 2.
FIG. 3A is a cross sectional elevation view of unassembled original cathode and anode lead terminals prior to assembling or fabricating process to form the conventional chip type solid state electrolytic capacitor of FIG. 1. FIG. 3B is a plan view of unassembled original cathode and anode lead terminals of FIG. 3A. The unassembled original cathode lead terminal 1 has a modified flat level with a step-like bent portion in cross sectional view. The unassembled original anode lead terminal 6 has a just flat level in cross sectional view. In plan view, the unassembled original cathode and anode lead terminals 1 and 6 have the same plan shape as each other.
Plural cathode lead terminals 1 extend from a cathode side lead frame portion 9a in a direction perpendicular to a longitudinal direction of the cathode side lead frame portion 9a. The plural cathode lead terminals 1 extend in parallel to each other and are aligned in a constant pitch in the longitudinal direction of the cathode side lead frame portion 9a. 
Each of the cathode lead terminals 1 has a plan shape which comprises a base portion 1a, a narrowed intermediate portion 1b and a top portion 1c. The base portion 1a extends from the cathode side lead frame portion 9a. The base portion 1a has a constant width. The base portion 1a is flat. The narrowed intermediate portion 1b extends from the base portion 1a. The narrowed intermediate portion 1b has a reduced width. The narrowed intermediate portion 1b is flat. The top portion 1c extends from the intermediate portion 1b. The top portion 1c has a rectangle shape with the same width as the base portion 1a. The top portion 1c is not flat, and is bent in step-like shape in cross sectional view. The top portion 1c has a top edge defined by a straight line parallel to the longitudinal direction of the cathode side lead frame portion 9a. 
Plural anode lead terminals 6 extend from an anode side lead frame portion 9b in a direction perpendicular to a longitudinal direction of the anode side lead frame portion 9b. The plural anode lead terminals 6 extend in parallel to each other and are aligned in a constant pitch in the longitudinal direction of the anode side lead frame portion 9b. This pitch is the same as the pitch of the cathode lead terminals 1.
Each of the anode lead terminals 6 has the same plan shape as the cathode lead terminals 1. The anode lead terminal 6 comprises a base portion 6a, a narrowed intermediate portion 6b and a top portion 6c. The base portion 6a extends from the anode side lead frame portion 9b. The base portion 6a has a constant width. The base portion 6a is flat. The narrowed intermediate portion 6b extends from the base portion 6a. The narrowed intermediate portion 6b has a reduced width. The narrowed intermediate portion 6b is flat. The top portion 6c extends from the intermediate portion 6b. The top portion 6c has a rectangle shape with the same width as the base portion 6a. The top portion 6c is flat. The top portion 6c has a top edge defined by a straight line parallel to the longitudinal direction of the anode side lead frame portion 9b. 
A set of the cathode side and anode side lead frame portions 9a and 9b, the plural cathode and anode lead terminals 1 and 6 forms a single lead frame 9.
FIG. 4A is a fragmentary plan view of an anode lead terminal which is weld-bonded through an pellet lead wire to a device pellet, wherein the pellet lead wire is parallel to the anode lead terminal. FIG. 4B is a fragmentary plan view of an anode lead terminal which is weld-bonded through an pellet lead wire to a device pellet, wherein the pellet lead wire is tilted with reference to the anode lead terminal.
As illustrated in FIG. 4A, the pellet lead wire 4 is parallel to the longitudinal direction of the anode lead terminal 6 and perpendicular to the top straight edge of the anode lead terminal 6. An overlap region 4d between the pellet lead wire 4 and the anode lead terminal 6 is the desired one. This desired overlap region 4d ensures a sufficient and uniform area for obtaining a sufficient and uniform weld-bonding strength.
As illustrated in FIG. 4B, the pellet lead wire 4 is not parallel to and tilted from the longitudinal direction of the anode lead terminal 6. The pellet lead wire 4 is not perpendicular to the top straight edge of the anode lead terminal 6. An overlap region 4c between the pellet lead wire 4 and the anode lead terminal 6 is the undesirable one. This undesirable overlap region 4e is smaller in area than the above desired one. This undesirable overlap region 4e obtains an insufficient and non-uniform area for obtaining an insufficient and non-uniform weld-bonding strength.
In order to avoid the problem shown in FIG. 4B, the length of the pellet lead wire 4 is increased to increase the overlap area 4e for the purpose of obtaining the sufficient and uniform weld-bonding strength. Under a condition of a fixed size of the case containing the capacitor, the increase in length of the pellet lead wire 4 needs a reduction in size of the device pellet 3.
It was proposed to increase the length of the anode lead terminal 6 for narrowing a gap between the device pellet 3 and the anode lead terminal 6 in order to increase the overlap area 4e for the purpose of obtaining the sufficient and uniform weld-bonding strength. Narrowing the gap between the device pellet 3 and the anode lead terminal 6 increases a possibility of undesired contact between the device pellet 3 and the anode lead terminal 6, whereby a short circuit is undesirably formed between the device pellet 3 and the anode lead terminal 6.
In order to avoid the contact between the device pellet 3 and the anode lead terminal 6, an insulating material is inserted into the gap between the device pellet 3 and the anode lead terminal 6. The gap size in this case is larger than the above narrowed gap size because the insulating material is inserted into the gap. The increase in the size of the gap also needs size reduction of the capacitor.
A further size reduction of the capacitor is desired. Further increases in the bonding strength and the bonding stability between the anode lead terminal and the pellet lead wire are also desired. The conventional technique is unable to obtain both the size reduction of the capacitor and the increases in the bonding strength and the bonding stability between the anode lead terminal and the pellet lead wire.
In the above circumstances, the development of a novel solid-state electrolyte capacitor free from the above problems is thus desirable.
Accordingly, it is an object of the present invention to provide a novel solid-state electrolyte capacitor free from the above problems free from the above problems.
It is a further object of the present invention to provide a novel solid-state electrolyte capacitor reduced in size and having increased bonding strength stability between an anode lead terminal and a pellet lead wire.
It is a still further object of the present invention to provide a novel anode lead terminal of the solid-state electrolyte capacitor free from the above problems.
It is yet a further object of the present invention to provide a novel anode lead terminal of the solid-state electrolyte capacitor reduced in size and having increased bonding strength stability between the anode lead terminal and a pellet lead wire.
The present invention provides a solid state electrolytic capacitor having an improved anode lead terminal having first and second side edges distanced from each other in a longitudinal direction of the anode lead terminal, wherein a center position on the first side edge is retracted from opposite side positions on the top edge, and the opposite side positions are distanced in a perpendicular direction to the longitudinal direction.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.